This invention pertains to a method for monitoring fetal-maternal circulation time and fetal-maternal respiratory kinetics as an indicator of the condition of a fetus during child-birth. More particularly, the method involves measurement of maternal circulation time and maternal-fetal circulation time by detecting transdermal respiration, at a selected point on the skin of the mother and at a point on the fetal scalp, of an identifiable gas inhaled by the mother. The method employs a monitoring system of a gas analyzer or detector comprising a mass spectrometer or an atomic absorption spectro-photometer connected to a sniffer probe attached by suction to the maternal and fetal skin.
The time during which the mother is in labor prior to birth is a critical period with regard to the health of the fetus. It is important to have immediate indication of any problem relating to the condition of the fetus caused by pathology of or changes in the utero-placental-fetal unit or because of some medical problem in the fetus itself. Difficulties in this unit can cause permanent damage or even threaten the life of the fetus. Examples of medical problems which can be encountered are blockage of the umbilical cord, placental dysfunction or abruption of the placenta, resulting in partial or total loss of oxygen to the fetus. In the mother, cardiac failure or obstructive pulmonary disease can reduce oxygen supply to the fetus. Physicians must be in a position to make rapid decisions during labor to protect the fetus from harm, including the decision of interrupting the natural birth process by performing a caesarian section.
There are currently several methods used to monitor the fetal condition during labor. One such method in common use involves an electronic fetal monitor (EFM). Examples of EFM methods and apparati are shown in U.S. Pat. Nos. 3,599,628, 3,367,323 and 3,409,737. In general, an EFM uses a recorder to register simultaneously the fetal heartbeat and uterine contractions. Ominous patterns, such as loss of beat to beat variability, sometimes can be discerned before labor. This is referred to as a non-stress test. Frequently, ominous patterns of the fetal heart rate are noticed during or immediately after contractions, for example, delayed decelerations or variable decelerations of the fetal rate. These patterns indicate possible trouble for the fetus. The evaluation of these ominous patterns can be difficult and the information provided is subject to misinterpretation. Secondary tests are often needed to accurately determine if fetal distress is actually occurring. One secondary method is to sample blood from an incision in the fetal scalp and measure the blood pH to diagnose fetal acidosis, a definite threat to the fetus. Alternatively, subcutaneous oxygen probes can be inserted to determine scalp p0.sub.2, although the technology to measure scalp p0.sub.2 is not sufficiently developed at this time to be in general use. These invasive methods create further hazards to the fetus by increasing the chances of infection. Because the ominous EFM patterns must be subjectively evaluated, it is believed that a much greater number of caesarian births are performed than are necessary.
Methods and apparati for measuring diffusion through the skin of gases insoluble in the blood stream are known in the literature. The gas can be inhaled or injected intravenously. An example of one type of transcutaneous physiological sensor apparatus is shown in U.S. Pat. No. 4,334,541.
Numerous gas detectors and analyzers are known, for example, the Varian Porta-Test (TM) helium leak detector 938-41 or the Inficon series mass spectrometer gas analyzers. These are used primarily in industry to test the security of tanks for gas leaks.